By the end of this century the seas may be three feet (one meter) higher than they are today, according to a pair of studies that appear in tomorrow's issue of the journal Science.

"After that we'll be committed to multiple more meters of sea level rise that will occur at rates of up to a meteror three feetper one hundred years," said Jonathan Overpeck, an earth scientist at the University of Arizona in Tucson, who co-authored the studies.

"And it could go faster," he added.

But scientists don't know if it will. They believe global warming triggered the ice's seaward gallop, but they say the dynamics at play are poorly understood.

"We did not expect that the ice sheets can react to warming on such a short time scale," said Konrad Steffen, a geographer at the University of Colorado at Boulder who has spent the past 15 years monitoring ice sheets in Greenland (map).

Scientists thought ice sheets and glaciers would respond to warming slowly over hundreds of years. The current acceleration could be a short-term adjustment to the warmer temperatures, Steffen said.

"Something dramatic is happening," said Göran Ekström, a seismologist at Harvard University in Cambridge, Massachusetts.

Ekström and colleagues report tomorrow in Science that glacial earthquakesseaward lurches of glaciersin Greenland have more than doubled in number since 2002.

Most of the glacial earthquakes occur in July and August, at the height of the Northern Hemisphere's summer melt.

The finding complements a study published in Science last month that found some of Greenland's glaciers have doubled in speed over the past five years, said Jay Zwally, a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.